Many of the mechanisms of self-renewal and differentiation of hematopoietic precursor cells, including the regulation of these processes, remain to be elucidated. In many respects, further detailed experimental analysis of hematopoiesis depends on the identification, isolation, and molecular characterization of pluripotent and committed hematopoietic precursor cells. Immunological identification and study of subsets of cells have led to dramatic progress in understanding other differentiating organ systems; and initial studies reveal impressive heterogeneity of myeloid cell surfaces that should allow manipulation by immunological probes. We propose further development and use of murine and human monoclonal antibodies specifically directed against small subsets of myeloid cells to approach the identification and isolation of human hematopoietic precursor cells. Several collectively unique approaches to antibody development and characterization will be employed. Resulting antibodies will be used to isolate precursor cells and to study hematopoiesis in model systems. This work might have eventual broad application for the understanding, diagnosis, and treatment of leukemia and aplastic anemia. We have shown that anti-My-1 and other antibodies against mature granulocytes do not react with the colony-forming cells for granulocytes and macrophages (CFC-GM). In contrast, the AHN-7 monoclonal antibody reacts with about 75% of CFC-GM revealing previously undescribed heterogeneity of CFC-GM. The anti-My-10 monoclonal antibody binds to 0 to 4% of normal human marrow nucleated cells. These My-10-positive marrow cells are predominantly morphologic blast cells. Both myeloid and erythroid progenitor cells express My-10, as do progenitors which form colonies of mixed lineages. In addition, early marrow lymphoid progenitors (defined by terminal deoxynucleotidyl transferase expression) express My-10, a 115 kilodalton glycoprotein. Thus, this is a prototype progenitor/blast cell antigen which may be of use for purification of stem cells for clinical bone marrow transplantation. The anti-My-11 monoclonal antibody recognizes a 230 kilodalton antigen which is expressed by lymphoid and myeloid but not erythroid or multipotent progenitor cells. My-11 appears, therefore, to define a commitment step in hematopoiesis. Further analysis of the cell populations isolated from marrow by these monoclonal antibodies is in progress. We hope this work will yield a detailed antigenic phenotype of myeloid colony-forming cells. (S)